The Raspberry Pi offers unique expandability through the 40-pin GPIO it features. The SparkFun Pi Wedge cables into this, and breaks the pins out to your breadboard. What's even of more use is the convenient FTDI-style USB-to-TTL connector on one end that lets you tap straight into the serial comms line of the Raspi for simple & quick monitoring of the terminal.

It's a pretty handy tool for doing hardware hacking with the Raspberry Pi.